Do you get attracted to other people while in relationship?

I don't mean it as in seeing someone and a knowledging they are good looking but as in being turned on by them or considering relationship with them or thinking what would it be like with them or be interested in them.

Recently this seems normal on the internet and I can't relate to it at all. If i see a handsome guy, I can say he is handsome but my boyfriend is still so much more handsome. And I only get turned on by my boyfriend. I have no need for anything that isnt platonic with other guys.